autogenerate MANIFEST (add to src tarball)
various mingw32 fixes (mingw64 is better)

tested with i586-mingw32msvc-gcc, i686-w64-mingw32-gcc and x86_64-w64-mingw32-gcc
all with CROSS=1

create bin earlier in config.mak make config.inc

optimize win32 to use cc only once to .o, no .opic
vasprintf needs ... decl and w64-mingw32 exceptions
pngc_page_delete() cannot cast a volatile to non-volatile (mingw32-gcc-4.2.1)
add some missing mingw32 includes (worked ok on mingw64)